This invention relates to a piston-type arc blow-out switch that includes a plurality of serially (tandem) arranged extinguishing units, for example, three per pole. The blow-out switch has, in a superposed relationship in insulating cylinders, several identical extinguishing chambers (switch unit modules) with movable compression cylinders and stationary compression pistons. The compression cylinders are driven, during switch actuation, by means of at least one actuator rod made of an insulating material.
In switches of the above-outlined type, all serially arranged switch units have to be simultaneously actuated with the application of a large force (for example, by means of a hydraulic drive) during the circuit breaking operation. During this operation the extinguishing (blow-out) medium which is usually SF.sub.6, is compressed prior to the contact separation proper. The movable compression cylinders and the switch contacts of the individual switch units are, for this purpose, coupled with an actuator rod made of an insulating material, while the compression pistons remain stationary with respect to the switch housing. During the circuit breaking operation a pulling force is exerted on the actuator rod, while during the circuit making operation a pressing force is exerted thereon. The individual switching chambers are usually surrounded by cylinders made of an insulating material for protecting the metallic switch housing against the arc generated during the circuit breaking operation.
A metal-encased switch of the above-outlined type is described, for example, in BROWN-BOVERI-MITTEILUNGEN, 1974, Vol. 4, page 157 (Bulletin issued by the Swiss firm Brown-Boveri). In the circuit breaker disclosed in this publication, the individual switch units are driven by a relatively thick actuator rod which is guided laterally externally of the switching chambers that are enclosed in the insulating cylinders. The actuator rod is composed of individual length portions having identical diameters. For effecting a mechanical connection of the actuator rod with the movable compression cylinders there are provided connecting elements which project through openings in the insulating cylinders. The actuator rod and the connecting elements are exposed, in addition to tension and pressure, to bending stresses as well. Consequently, they must have a non-changing large diameter or, as the case may be, should be tubular components.